When load is applied to a concrete floor slab of a bridge due to traffic or the like. Acoustic Emission (AE) occurs due to crack propagation, friction, or the like in the floor slab. AE can be detected by installing an AE sensor on a surface of the floor slab. AE is an elastic wave generated as a fatigue crack of a material develops. Further, by installing a plurality of AE sensors, a source location of the elastic wave (hereinafter referred to as “AE source”) can be calculated from a difference in AE arrival time between the sensors.
Generally, in a concrete floor slab of a bridge, although damage inside the floor slab such as horizontal cracks is very difficult to detect by conventional nondestructive inspection, the damage inside can be estimated by analyzing data acquired by the AE sensors. However, a large amount of time is required for installing an AE sensor in a bridge and the like and obtaining sufficient data for estimating damage thereto. Therefore, an inside of concrete cannot be evaluated efficiently in some cases. Such a problem is not limited to the concrete floor slab of a bridge but is a problem common to all the structures in which elastic waves are generated as cracks occur or develop.